The present invention relates to a thin film transistor and a method for manufacturing the transistor and more particularly, to an image display device having such thin film transistors built therein and a method for manufacturing the display device.
With respect to a TFT type liquid-crystal display device having thin film transistors (which will be referred to as TFT's, hereinafter), there is disclosed a TFT liquid-crystal display device with a circuit built therein (which will be also referred to as the circuit built-in type TFT liquid-crystal display device, hereinafter) wherein a pixel switching element and a display pixel region peripheral circuit make up a polycrystalline silicon TFT, e.g., in JP-A-64-2088.
There is also disclosed such a circuit built-in type TFT liquid-crystal display device, for the purpose of attaining a high circuit performance, which is improved in its TFT mobility by growing a silicon crystal largely in a specific direction to align a source/drain arrangement direction (current direction) nearly with the longitudinal direction of crystal grains, e.g., in JP-A-11-121753.
Further, in such a liquid-crystal display device as disclosed in an embodiment of, e.g., JP-A-2000-243970, a TFT source/drain arrangement direction (current direction) is aligned nearly with the longitudinal direction of crystal grains, and respective TFT's are arranged in horizontal and vertical blocks (in horizontal and vertical directions) at a display pixel array periphery when the TFT's are viewed from the front side surface of an array substrate. However, this display device fails to show a specific example of the TFT arrangement.
In the aforementioned JP-A-11-121753 of the TFT type wherein the current direction from the drain to the source is aligned nearly with the longitudinal direction of crystal grains, the performance of each TFT can be improved. However, since the current direction is limited to the horizontal (horizontal block) direction or vertical (vertical block) direction, this restricts the TFT array when layout design is made about a pixel array or a peripheral circuit, thus increasing a circuit occupation surface area.
In order to avoid such restriction to some extent, in the case of the embodiment shown in FIG. 1 in the aforementioned JP-A-2000-243970, laser irradiation is carried out in two horizontal and vertical directions, so that TFT's are arranged in the horizontal (horizontal block) direction and in the vertical (vertical block) direction. In the known example, when the TFT array is viewed on an identical straight line of the horizontal or vertical direction, the horizontal direction TFT's are arranged as not mixed with the vertical direction TFT's in the source/drain arrangement direction (current direction), no TFT is formed by laser irradiation so as to be arranged at a corner of the display device and at a pixel array, which results in limitation of a high-performance TFT array.